Conventionally, a gas sensor is installed in an exhaust pipe of an internal combustion engine to measure a concentration of a specified gas, for example Oxygen or NOx, in exhaust gasses.
FIG. 15 shows an example of such a gas sensor. A gas sensor 9 includes a hollow cylindrical housing 10 having a flange 100, a sensing element 19 fixed in the housing 10, a protective cover 11 disposed on a first end of the housing 10, and an outer cover 12 disposed on a second end of the housing 10. A first end of the gas sensor 9 is inserted into a fitting hole 30 formed in an exhaust pipe 3. A washer 102 is disposed between a first end 101 of the flange 100 and an outer surface 301 around the fitting hole 30 of the exhaust pipe 3.
Recently, the amount of heat conducted from a first end to a second end of a gas sensor has increased, since a temperature of exhaust gasses has become higher. However, a gas sensor generally includes less heat-resistant parts, for example a water-repellent filter 123 or a rubbery insulator 15 as shown in FIG. 15.